Recovering as an ammonium salt the nitrogen of the hydrocyanic acid in crude coal-gas.



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EDWARD VICTOR EVANS, OF LONDON, ENGLAND, ASSIGNOR TO SOUTH METROPOLITAN GAS-COMPANY, OF LONDON, ENGLAND. f

RECOVERING AS AN AMMONIUIVLSALT THE NITROGEN OF THE HYDROCYANIC ACID IN CRUDE COAL-GAS,

To all whom it may concern Be it known that I, EDWARD VICTOR EVANS, a subject of the King of Great Britain, residingin London, England, have invented certain new and useful Improvements in Recovering as an Ammonium Salt the v Nitrogen of the Hydrocyanic Acid in Crude and Klason in 1887 investigated the reaction Coal-Gas, ofavhich the following is aspecification.

A known process for disposing of the hydrocyanic acid present in crude coal gas consists in absorbing the hydrocyanic acid in the forni of ammonium sulfocyanid and then treating the latter so as to convert the cyanogen nitrogen into ammonia which may be worked up with the ammonia present as such in the crude gas. 7

Among methods of treating the ammonium sulfocyanid for the object in question, heating it with sulfuric acid has been mentioned. No directions for obtaining ammonia in this manner have been given, howeverfeither in this connection or in any other save in the scientific investigation hereinafter cited. It is known that some of the nitrogen in a sulfocyanid is'convert-ed into ammonia when the salt is hydrolyzed, while? some'of the carbon becomes carbon oxysulfid or carbon dioxid. e t

The chemical change is generally represented by the equation from the point'of View of the conditions under which it -must occur in order that the yield of carbon oxysulfid may be a maximum.

I have found that these conditions arenot such as are suitable for the maximum yield of ammonia, (which latter is obtained, of course, in the form of a salt of the acid I used for "hydrolysis. f 1

,Temperatureis the most important condition for my purpose. With regard to this factor Klason merelystates that the efiect of temperature on his reaction is only'toincrease its velocity as the.temp'erature is g'raised, I have foundflthat the temperature Specification of Letters Patent.

production of bodies containing nitrogen of the type of thiocarbamic acid, which, as

may be gathered from 'Klasons statement,

Patented July 2'7, 119115.

Application filed July-30,'1914. Serial No. 854,173.

are inevitably formed as products of the reaction, may be substantially avoided and a parable with that represented by the fore going equation. This was not to be foreseen, since Klason has stated that these nitrogenous' compounds resist the attack of evensstrong acids at the temperature of the water bath.

- According to the present invention, therefore, the ammonium sulfocyanid made from the hydrocyanic acid in crude coal gas is hydrolyzed by an acid, preferably sulfuric acid, at a temperature not lower than 50 Q, and under conditions-of concentration and proportion by mass suitable for obtaining the maximum yield of ammonia in the form of an ammonium salt.

The best temperature can only be ascertained by experiment when it has been decided what is to be the proportion of ammonium sulfocyanid to acid,.and what is to be the degree-of dilution of the mixture undergoing reaction. These conditions vary with the nature of the coal carbonized to produce the coal gas, the mode of carbonization and the particular process adopted for absorbing the hydrocyanic acid in the form of ammonium sulfocyanid, in short -with the practice of gas works or coke oven installation where the invention is applied. The invention is primarily intended for gas-works or coke oven works where am 'monia is used for making ammonium S111 fate forhere it is convenient to use sulfuric acid for the hydrolysis and owing to the fact that excess of acid must be used for obtaining 'the best yieldof ammonia, the liquor produced by the hydrolysis is a suitable liquor for feeding .the saturator of thexam C., since this is best for. the conditions likely to prevail whenordinary. gas coals are used, namely (1) An extraction of some 95 the cyanogen in the crude gas inthe-form of a solution of ammonium sulfocyanid of per cent. of

20-30 per cent. strength,- (2) the use of sulfuric acid of 7080 per cent. strength for the ammonium sulfate saturator; (3) such a proportion-of ammonia in the gas that if the acid in the saturator is to be equivalent.

toboth this ammonia in a given volume of the gas and that equivalent to the ammonium jacket or otherwise;

'sulfocyanid produced from the cyanogen in that volume, the volume .of acid (of the above strength) used to hydrolyze the sulfocyanid should bear the ratio to the volume of ammonium sulfocyanid solution -(of the above strength) of about 1.5 1. Thus, with an ammonium sulfocyanid solution -of 30 per cent. strength the following procedure may be expected to give some 9699 per cent; of the theoretical yield of ammonia as calculated from the foregoing :equation, and

this ammonia will be contained inan acid liquor suitable for the saturator of ltheammonium sulfate plant, that is to say, the liquor afterth-e hydrolysis reaction will con- .tain so much'free acid that when saturated with the gases evolved in the ammonia stills solution to that of theacid is 121.5. Thestirrer is worked vigorously throughout the operation and the temperature of the liquid ismaintained at 80-90 C., by a steam Since there are so many variable conditions aflecting the-process, it is practically Impossible to set forth the best procedure for all conditions. The following experimental work, however, may be prescribed for those wishing to ascertain the best conditio'ns'for the particular strength of sulfocyanid solution 'orsulfuric acid which is to be used. y b

Assuming that a test made on the lines of the foregoing example with the sulfocyanid solution and sulfuric acid at disposal fails to 'give a satisfactory yield of ammonia (say vessel produces 'aprecipitate.

event the temperature of the reactionshould about 96 per cent.),'the nitrogen escaping hydrolysis may be found either in the form of a precipitate in the vessel or may have' escaped as agas during the reaction. The first observation to be made in. this case is whether or not there is a precipitate in ,the reaction" vessel or considerable dilution with vwater of the liquor of the reaction In either be increased until that is found which insures the absence of la precipitate; another I v method ofa'voiding 'a precipitate is to increase V tilization is considerable.

mixture, and there remains an ineflicient yield of ammonia, it is an indication that the quantity of nitrogenous gases lost by vola- To overcome this a larger relative volume of acid, or acid of higher concentration should be used. It is obvious that a lower concentration of sulfocyanid solution would effect the same result. To exemplify this, if an inefiicient yield is obtained by hydrolysis, and no precipitate is formed, it is generally an indication that the temperature maintained during the reaction is too high. If on reducing the temperature, a precipitate occurs before the eflicient yield of ammonia is attained, then the volume or strength of the acid must be increased, or the sulfocyanid solution diluted.

The precipitate herein mentioned should not be confused with a small quantity of sulfur which is sometimes produced (especially with concentrated acids) as the result of the reducing actionvof sulfureted hydrogen. Its nature has not been fully investigated, but it is considered to be a mixture of persulfocyanic acid and certain s'ulfided compounds of thiocarbamic acid.

Having thus described my invention and the best means I know of carrying the same into practical eflect, I claim 1. A process for recovering in the form ofan ammonium salt the nitrogen of the hydrocyanic acid in crude coal gas, which process consists in first converting the hydrocyanic acid into ammonium sulfocyanid and then heating the ammonium sulfocyanid at a temperature above 50 C. with such a proportion of water and acid that no appreciable precipitate is produced in the liquor and that no appreciable volatile nitrogenous products escape.

2.v A process for recovering in the form of an ammonium salt the nitrogen of the hydrocyanic acid in crude coal gas which process consists in first converting the hydrocyanic acid into ammonium sulfocyanid and then heating the ammonium sulfocyanid at .a temperature above 50 C. with such a pro-.

portion of Water and sulfuric acid that no appreciableprecipitate is produced in the liquor and that no appreciable volatile ni-' trogenous products escape. 3. A process for recovering 1n the form of an ammonium salt the nitrogen of the hydrocyanic acid in crude coal gas, which procduced from-the ammonium sulfocyanid' by this heating and tothe ammonia in the volume of gas from which the sulfocyanid has been-made, and finally introducing the liquor thus produced into the saturator of the apparatus in which the ammon-iacal liquor produced from the said gas is distilled.

*1. A process for recovering in the form of an ammonium salt the nitrogen of the hydrocyanic acid in crude coal gas, which process consists in first converting the hydrocyanic acid into ammonium sulfocyanid .solution of 20 30 per cent. strength and then heating this solution at 80110 O.- with one and a half times. its volume ofsulfuric acid of 70-80 per cent. strength.

In testimony whereof I have signed my name to this specification in the presence of. two subscribing witnesses.

EDWARD VICTOR EVANS.

Witnesses JOSEPH MILLARD, W. J! SKERTEN. 

